Field of the Invention
The present invention concerns a display device and, particularly, it relates to a liquid crystal display device of an in-plane electric field system (IPS) excellent in view angle characteristics with no image unevenness also at the periphery of a display region.
Description of Related Art
In a liquid crystal display device, a TFT substrate having pixel electrodes and thin film transistors (TFT) formed in a matrix and a counter substrate opposed to the TFT substrate and having color filters, etc, formed at portions corresponding to the pixel electrode of the TFT substrate are disposed, and liquid crystals are put between the TFT substrate and the counter substrate. Then, images are formed by controlling the transmittance of a light by liquid crystal molecules on every pixel.
Since the liquid crystal display device is flat and light in weight, application use thereof has been extended in various fields. Small-sized liquid crystal display devices are generally used for cellular phones, DSC (Digital Still Cameras), etc. In the cellular phones and DSC, there exists a demand of enlarging the size of the display screen while keeping the outer shape of a liquid crystal display device small. Then, a so-called frame at the periphery of the display region is reduced. In such a constitution, the periphery of the display region tends to undergo the effect of potential fluctuation at, etc. at the frame portion.
On the other hand, view angle characteristics become a problem in the liquid crystal display devices. The view angle characteristics concern a phenomenon that the luminance or chromaticity changes between a case of observing a screen at the front and a case of observing the screen obliquely. For the view angle characteristics, an IPS (in plane switching system) of operating liquid crystal molecules by an electric field in a horizontal direction has excellent characteristics.
Japanese Unexamined Patent Publication No. 2005-275054 describes a liquid crystal display device of the IPS system in which a tapered portion of scanning line leads is covered with a conductive film by way of an insulative film so that blanking does not occur at the periphery of a display region by noises from the scanning line leads. That is, a pitch in the terminal portion for connecting the scanning lines with external circuits is smaller than the pitch of the scanning lines formed in the display region. Then, the scanning line leads that connect the terminal portion with the scanning lines of the display region are in the form of oblique (tapered) wirings for adjusting the pitch between the display region and the terminal portion. In the oblique wiring portion, since the wiring density is higher than that in the display region and noises due to scanning signals tend to be generated, it is intended to cover the portion with the conductive film thereby reducing the effect of the noises from the tapered portion in JP-A No. 2005-275054. For the conductive film, ITO (indium tin oxide) which is identical with that used for the pixel electrode is used.
In the constitution descried in JP-A No. 2005-275054, the scanning line lead is covered with ITO which is identical with that used for the pixel electrode. In a case of covering the scanning line lead with ITO, close adhesion between ITO and a sealant causes a problem. An epoxy resin is generally used for the sealant. The sealant has good adhesion with an insulative film such as made of SiN and can maintain a favorable sealing property. However, in a case where the sealant is in direct contact with the conductive film such as an ITO film, reliability of sealing is not always known.
As in the constitution described in JP-A No. 2005-275054, when the scanning line lead is covered with ITO that is formed at the same time with the pixel electrode, this causes a problem for the reliability depending on the relation between ITO and the sealant. Further, while the extent of covering the region of the peripheral ITO gives a significant effect on the shielding effect to the scanning line leads, JP-A No. 2005-275054 has no descriptions for such a problem.
Further, in the constitution of JP-A No. 2005-275054, since ITO used for shielding the scanning line lead is identical with that used for the pixel electrode, it can not be formed continuously from the display region, to result in a portion where the scanning line lead is not covered with ITO at the boundary between the scanning line and the scanning line lead portion. Then, the effect of scanning signals is generated from the portion not covered with ITO.
The present invention intends to eliminate blanking due to the effect of scanning in the display region in a liquid crystal display device of the IPS system, while maintaining the sealing reliability by a sealant.